IDI2, a Second Isopentenyl Diphosphate Isomerase in Mammals

Daun B Clizbe,Michelle L Owens,Kimberly R Masuda,Janis E Shackelford,Skaidrite K Krisans

doi:10.1074/jbc.m610922200

Daun B Clizbe, Michelle L Owens + Show 3 more

Open Access

https://doi.org/10.1074/jbc.m610922200

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Abstract

We recently described the identification of a novel isopentenyl diphosphate isomerase, IDI2 in humans and mice. Our current data indicate that, in humans, IDI2 is expressed only in skeletal muscle. Expression constructs of human IDI2 in Saccharomyces cerevisiae can complement isomerase function in an idi1-deficient yeast strain. Furthermore, IDI2 has the ability to catalyze the isomerization of [(14)C]IPP to [(14)C]DMAPP. Enzyme kinetic analysis of partially purified IDI2 demonstrate the novel isozyme has a maximal relative specific activity of 1.2 x 10(-1) +/- 0.3 micromol min(-1) mg(-1) at pH 8.0 with a K(IPP)(m) value of 22.8 microm IPP. Both isozymes, IDI1 and IDI2 are localized to the peroxisome by a PTS1-dependent pathway. Finally, our data suggest that IDI2 is regulated independently from IDI1, by a mechanism that may involve PPARalpha.

Highlights

All isoprenoids are derived from the 5-carbon isoprene defined by isopentenyl diphosphate (IPP) and its highly electrophilic isomer dimethylallyl diphosphate (DMAPP)
Simultaneous probing indicates that IDI2 is expressed at a notably higher level than IDI1 in skeletal muscle (Fig. 1A, panel c)
In agreement with Northern data, the quantitative real-time PCR (QRT-PCR) data illustrate that IDI2 is present only in skeletal muscle and expressed at higher levels than IDI1

Summary

Introduction

All isoprenoids are derived from the 5-carbon isoprene defined by isopentenyl diphosphate (IPP) and its highly electrophilic isomer dimethylallyl diphosphate (DMAPP). Our data illustrate that IDI2 has a distinct tissue expression pattern, has functional isomerase activity in vivo, a unique kinetic profile, and is targeted to the peroxisome by a PTS1-dependent pathway. Cholesterol Synthesis Assay—Cholesterol, fatty acid, and dolichol phosphate rate of synthesis was determined using the method previously described [13] with the following modifications: 100-mm cell culture plates were seeded with 2 ϫ 105 C2C12transfected cells with either vector-only or pcDNA3.1IDI2 vector.

Results

Conclusion